ICP mass analysis devices are widely known as analyzers capable of performing high sensitivity multi-element analysis, and are used for elemental analysis in a broad range of fields (for example, see Patent Literature 1). FIG. 6 illustrates the general device configuration of an ICP mass analysis device.
ICP mass analysis device 100 mainly comprises a plasma torch 11, a high frequency power supply 12, a sample introduction unit 13, a mass analysis unit 14 comprising a mass analyzer, a gas flow rate control unit 15, and a device main body control unit 16, which make up a device main body unit 1. A cooling water system 2 and an Ar gas supply system 3, which are necessary when using the ICP mass analysis device 100, are furthermore connected to the device main body unit 1.
The device main body unit 1 of the ICP mass analysis device 100 will be described in detail. The gas flow rate control unit 15 performs flow rate control of sample gas supplied from a nebulizer 19, Ar gas for plasma generation supplied via gas pipe 31 from the Ar gas supply system 3, and the like. The plasma torch 11 comprises a multiwall cylindrical reaction tube 17 to which plasma gas (Ar gas) and sample gas are supplied under flow rate control by the gas flow rate control unit 15, and a high frequency coil 18 wound onto the outer circumference of the reaction tube 17.
The high frequency power supply 12 is connected to a high frequency coil 18, and plasma is generated to ionize the sample gas by applying high frequency voltage to the high frequency coil 18 in a state where plasma gas and sample gas have been introduced into the plasma torch 11.
The sample introduction unit 13 is kept in a reduced pressure state by means of a vacuum pump (not illustrated) and is designed to draw in ions of the sample, which has been ionized by the plasma torch 11, along the central axis of a sampling cone 13a through a sample introduction orifice. The mass analysis unit 14 is maintained at a higher vacuum than the sample introduction unit 13, and performs mass separation of the sample ions, which have been draw in from the sample introduction unit 13, by means of a quadrupole 14a or the like, and further performs mass analysis by means of an ion detector 14b. 
The device main body control unit 16 is composed of a computer device comprising an input device (keyboard, mouse, etc.), display device (liquid crystal panel, etc.) and input/output interface, and performs configuration, command input and control of the various units of device main body unit 1, and also performs processing of data detected by the ion detector 14b. 
In this sort of ICP mass analysis device 100, the reaction tube 17 of the plasma torch 11 which generates plasma is brought to a high temperature through induction heating, and in addition to that, the sample introduction unit 13 located opposite the plasma torch 11, the high frequency coil 18 and the high frequency power supply board 12a contained within the high frequency power supply 12 also reach a high temperature.
Thus, excluding the reaction tube 17 of the plasma torch 11, cooling is required for the sample introduction unit 13, high frequency coil 18 and high frequency power supply 12, and cooling water is supplied from a cooling water system 2 in order to prevent corrosion and melting of the copper sampling cone 13a of the sample introduction unit 13 and of the copper high frequency coil 18, and to prevent breakdown due to heat generation of the high frequency power supply board 12a contained within the high frequency power supply 12.
FIG. 7 is a drawing illustrating the piping system of cooling water system 2 and Ar gas supply system 3. The water-cooling piping of the cooling water system 2 is connected from a chiller (water source) 20 having a circulation pump which feeds cooling water, via a flow passage 21 to a master valve V0. The downstream side of the master valve V0 is connected to a flow passage 22, and the flow passage 22 branches in two and is connected to a first intermediate valve V2 and a second intermediate valve V3. A flow passage (bypass flow passage) 23 leading to the high frequency power supply 12 is connected to the first intermediate valve V2. A flow passage (high frequency power supply cooling flow passage) 24 for cooling the high frequency power supply 12 (high frequency power supply board 12a) is connected to the second intermediate valve V3.
Flow passage (bypass flow passage) 23 and flow passage (high frequency power supply cooling flow passage) 24 are used by switching between them so as to prevent condensation from forming on the high frequency power supply 12, and are controlled such that the flow passage 24 side is opened when the high frequency power supply is in an ON state and requires cooling, and the flow passage 23 side is opened when the high frequency power supply is in an OFF state and does not require cooling. This flow passage switching control is performed by the device main body control unit 16 in a manner interlocked with the turning on and off of the high frequency power supply 12, with control being performed such that when one is opened, the other is closed, so that cooling water is always flowing.
Flow passage 23 and flow passage 24 merge into flow passage 25, which then again branches into two and is connected to a flow passage (sample introduction unit cooling flow passage) 26 which cools the sample introduction unit 13 and a flow passage (high frequency coil cooling flow passage) 27 which cools the high frequency coil 18. After cooling the sample introduction unit 13 and high frequency coil 18, the flow passage 26 and flow passage 27 merge again into flow passage 28, and flow passage 28 is recirculated to the chiller 20.
The portions of device main body unit 1 which require cooling by the cooling water system 2 will be referred to as “cooled structures.” Among the three cooled structures consisting of the high frequency power supply 12, sample introduction unit 13 and high frequency coil 18, in the sampling cone 13a of the sample introduction unit 13, the orifice diameter of the central sample introduction orifice gradually widens due to aging degradation, which has an effect on analysis results, so the sampling cone 13a is made replaceable as a consumable part.
FIG. 8 is a simplified cross-sectional view illustrating the sample introduction unit 13. The sampling cone 13a is integrally mounted on the outer surface side of cooling jacket 13b, and the inner surface side of the cooling jacket 13b is removably secured across a seal (not illustrated) so as to make the interface with the sample introduction unit main body 13c liquid-tight. A cooling flow passage 13d through which cooling water flows is formed in the cooling jacket 13b, and cooling water is supplied via a connecting flow passage 13e provided in the sample introduction unit main body 13c. 
When the sampling cone 13a is to be replaced, the replacement is made from the cooling jacket 13b, and thus when the cooling jacket 13b is detached from the sample introduction unit main body 13c, the cooling water flow passage is opened at the interface between the connecting flow passage 13e and cooling flow passage 13d. 
If the cooling jacket 13b is to be detached in order to replace the sampling cone 13a after cooling water has been fed into the cooling water system 2, it is necessary to stop the supply of water by closing the master valve V0, and to perform purging in order to drain the residual water remaining in the various flow passages past the master valve V0. For this purpose, a flow passage for supplying purge gas is formed in the cooling water system 2.
Namely, as shown in FIG. 7, a purge gas flow passage 32 is formed, which branches off from the middle of the Ar gas flow passage 31 of the Ar gas supply system 3 and is connected at merging point G to the flow passage 22 downstream of the master valve V0 of the cooling water system 2. A purge valve V1 is provided in the purge gas flow passage 32, and a check valve GV which prevents cooling water backflow is interposed.
When the cooling jacket 13b of the sample introduction unit 13 is to be replaced, first, the master valve V0 is closed, after which the purge valve V1, first intermediate valve V2 and second intermediate valve V3 are all opened simultaneously, residual water is drained by introducing Ar gas from purge gas flow passage 32 into flow passages 22 through 28, and then the cooling jacket 13b is removed.
Similar Ar gas purging is also performed when performing maintenance operations of the cooling water system 2 besides the sample introduction unit 13. Furthermore, a similar draining operation using Ar gas purging is performed not just during maintenance operations but also in order to prevent corrosion due to residual water when the device is stopped for a long period of time.